Height Checker

Description

A school is trying to take an annual photo of all the students. The students are asked to stand in a single file line in non-decreasing order by height. Let this ordering be represented by the integer array expected where expected[i] is the expected height of the ith student in line.

You are given an integer array heights representing the current order that the students are standing in. Each heights[i] is the height of the ith student in line (0-indexed).

Return the number of indices where heights[i] != expected[i].

Example 1:

Input: heights = [1,1,4,2,1,3] Output: 3 Explanation: heights: [1,1,4,2,1,3] expected: [1,1,1,2,3,4] Indices 2, 4, and 5 do not match.

Example 2:

Input: heights = [5,1,2,3,4] Output: 5 Explanation: heights: [5,1,2,3,4] expected: [1,2,3,4,5] All indices do not match.

Example 3:

Input: heights = [1,2,3,4,5] Output: 0 Explanation: heights: [1,2,3,4,5] expected: [1,2,3,4,5] All indices match.

Constraints:

• 1 <= heights.length <= 100
• 1 <= heights[i] <= 100

Code

Time Complexity: $O(N)$, Space Complexity: $O(N)$

class Solution {
public:
    int heightChecker(vector<int>& heights) {
        vector<int> fre(101, 0);
        for(auto h: heights) {
            fre[h]++;
        }
 
        int index = 0;
        int res = 0;
        for(int i = 0; i < 101; i++) {
            while(fre[i] > 0) {
                if(i != heights[index++]) res++;
                fre[i]--;
            }
        }
        
        return res;
    }
};

Source

• Height Checker - LeetCode